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    SubjectRe: [PATCH] BSD Jail LSM (3/3)
    Attached is a patch carrying the documentation for the bsdjail LSM.

    Please apply.

    Signed-off-by: Serge E. Hallyn <>

    diff -Nru /home/hallyn/kernels/linux- linux-
    --- /home/hallyn/kernels/linux- 1969-12-31 18:00:00.000000000 -0600
    +++ linux- 2004-09-10 14:12:59.163385088 -0500
    @@ -0,0 +1,99 @@
    +BSD Jail Linux Security Module
    +Serge E. Hallyn <>
    +Implements a subset of the BSD Jail functionality as a Linux LSM.
    +What is currently implemented:
    + If a proces is in a jail, it:
    + 1. Is locked under a chroot (as are all children) which is not
    + vulnerable to the well-known chdir(..)(etc)chroot(.) escape.
    + 2. Cannot mount or umount
    + 3. Cannot send signals outside of jail
    + 4. Cannot ptrace processes outside of jail
    + 5. Cannot create devices
    + 6. Cannot renice processes
    + 7. Cannot load or unload modules
    + 8. Cannot change network settings
    + 9. May be assigned a specific ip address which will be used
    + for all it's socket binds.
    + 10. Cannot see contents of /proc/<pid> entries of processes not in the
    + same jail. (We hide their existence for convenience's sake, but
    + their existance can still be detected using, for instance, statfs)
    + 11. Has no CAP_SYS_RAWIO capability (no ioperm/iopl)
    + 12. May not share IPC resources with processes outside its own jail.
    + 13. May find it's valid network address (if restricted) under
    + /proc/$$/attr/current.
    +The security of this module is very much dependent on the security
    +of the rest of the system. You must carefully think through your
    +use of the system.
    +Some examples:
    + 1. If you leave /dev/hda1 in the jail, processes in the
    + jail can access that filesystem (i.e. /sbin/debugfs).
    + 2. If you provide root access within a jail, this can of
    + course be used to setuid binaries in the jail. Combined
    + with an unjailed regular user account, this gives jailed
    + users unjailed root access. (thanks to Brad Spender for
    + pointing this out). To protect against this, use jails
    + in private namespaces, with the jail filesystems mounted
    + ONLY within the jail namespaces. For instance:
    +$ # (Make sure /dev/hdc5 is not mounted anywhere)
    +$ new_namespace_shell /bin/bash
    +$ mount /dev/hdc5 /opt
    +$ mount -t proc proc /opt/proc
    +$ echo -n "root /opt" > /proc/$$/attr/exec
    +$ echo -n "ip" > /proc/$$/attr/exec
    +$ exec /bin/sh
    +$ sshd
    +$ apachectl start
    +$ exit
    +How to use:
    + 1. modprobe bsdjail
    + [ 1.5 /sbin/ifconfig eth0:0;
    + 1.6 /sbin/route add -host dev eth0:0
    + (optional) ]
    + 2. Make sure the root filesystem (ie /dev/hdc5) is not mounted
    + anywhere else.
    + 3. exec_private_namespace /bin/sh
    + 4. mount /dev/hdc5 /opt
    + 5. mount -t proc proc /opt/proc
    + 6. echo -n "root /opt" > /proc/$$/attr/exec
    + echo -n "ip" > /proc/$$/attr/exec (optional)
    + 7. exec /bin/sh
    + 8. sshd
    + 9. exit
    +The new shell will now run in a private jail on the filesystem on
    +/dev/hdc5. If proc has been mounted under /dev/hdc5, then a "ps -auxw"
    +under the jailed shell will show only entries for processes started under
    +that jail.
    +If a private IP was specified for the jail, then
    + cat /proc/$$/attr/current
    +will show the address for the private network device. Other network
    +devices will be visible through /sbin/ifconfig -a, but not usable.
    +If the reading process is not in a jail, then
    + cat /proc/$$/attr/current
    +returns information about the root and ip * for the target process,
    +or "Not Jailed" if the target process is not jailed.
    +Cat /proc/$$/attr/exec gives a list of the valid keywords to cat into
    +/proc/$$/attr/exec when starting a jail.
    +Current valid keywords for creating a jail are:
    + root: Root of jail's fs
    + ip: Ip addr for this jail
    + nrtask: Number of tasks in this jail
    + nice: The nice level for this jail. (maybe should be min/max?)
    + slice: Max timeslice per process
    + data: Max size of DATA segment per process
    + memlock: Max size of memory which can be locked per process
     \ /
      Last update: 2005-03-22 14:06    [W:0.023 / U:13.224 seconds]
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